Abstract:

Piezoelectric fan is a solid-state device which generally consists of a patch of piezoelectric material and a flexible blade. It employs the reversed piezoelectric effect to make the piezoelectric patch expand and contract periodically, driving the attached flexible blade to oscillate at the same frequency. Due to the oscillatory motion of flexible blade, the neighboring fluid is periodically excited and thus a pseudo-jet or streaming flow is produced shedding along the fan tip. On account of its some features, such as simple structure, low power consumption, and easy controllability, piezoelectric fan has recently gained much attention in the practical applications, such as electronics cooling, energy harvesting, biomimetic robotic propulsion, etc. Innovation on heat transfer enhancement with active flow control technology is a frontier issue aspect facing to the engineering thermal science. The effects of α (the angle between vibrating direction and cross flow direction) and u (cross flow velocity) on the amplitude of a single piezoelectric fan have been tested by using Laser Doppler Vibrameter (LDV). Three-dimensional unsteady flow and heat transfer characteristics driven by single piezoelectric fan arranged normally to the heated surface with different β (the angle between piezoelectric fan center line and cross flow direction) was per-formed by using dynamic meshing scheme. The displacement of the vibrating fan was determined from vibration test by using LDV. An experimental test for the local convective heat transfer coefficient distribution was also made by using infrared camera. The results show that aerodynamic loading from cross flow gets minimum and the amplitude of the piezoelectric fan is maximum when α equals 90°. When β equals 90°, the vortical structures excited by the coupling effect of piezoelectric fan and cross flow impacts the heated surface, and the shed-ding vortex is easier to be broken down in downstream region in relative to the other cases. In this condition, the local convective heat transfer in fan-tip vibration envelope is effectively enhanced, and the coupled heat transfer performance is 2 times larger than β=45° and 135°. The cycle-averaged local heat transfer coefficient distribution obtained by tested is well consistence to the numerical simulation.

Key words: piezoelectric fan, heat transfer, vibration test, numerical simulation, experimental validation

摘要：

利用激光多普勒测振仪分别测定攻角和横流速度对压电风扇振幅的影响。基于相应的振动测试结果利用动网格技术对横流环境中不同安装角度下压电风扇冷却加热壁面的三维非定常流动和传热特性进行了数值模拟，同时应用红外热像仪对相同横流条件工况下加热表面的局部对流传热系数分布进行了测量。研究结果显示，攻角为90°时，作用在风扇上的气动载荷最小，风扇振幅最大，而随着攻角的减小风扇振幅也逐渐减小；安装角为90°时，压电风扇振动以及横流作用所诱导形成的耦合涡结构冲击加热表面，并在下游区域具有明显的脱落、破碎过程，对于叶尖包络区对应的壁面局部对流换热有显著的强化作用，此时风扇耦合换热性能最强，高于45°和135° 2倍以上；且时均对流传热系数的实验结果与数值模拟具有良好的一致性。

关键词: 压电风扇, 传热, 振动测试, 数值模拟, 实验验证